Package-on-Package Process for Applying Molding Compound

ABSTRACT

A method of packaging includes placing a package component over a release film, wherein solder balls on a surface of the package component are in physical contact with the release film. Next, A molding compound filled between the release film and the package component is cured, wherein during the step of curing, the solder balls remain in physical contact with the release film.

BACKGROUND

In a conventional package-on-package (POP) process, a top package, in which a first device die is bonded, is further bonded to a bottom package. The bottom package may also be bonded with a second device die. As a result, the second device die may be on the same side of the bottom package as the solder balls that are used to bond the bottom package to the top package.

Before the bonding of the top package to the bottom package, a molding compound is applied on the bottom package, with the molding compound covering the second device die and the solder balls. Since solder balls are buried in the molding compound, a laser ablation or drilling is performed to form holes in the molding compound, so that the solder balls are exposed. The top package and the bottom package may then be bonded through the solder balls in the bottom package.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the embodiments, and the advantages thereof, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which:

FIGS. 1 through 4 are cross-sectional views of intermediate stages in the formation of a top package in accordance with an embodiment;

FIGS. 5 through 7 are cross-sectional views of intermediate stages in the formation of a bottom package in accordance with an embodiment, wherein a compressive molding method is used to apply a molding compound;

FIGS. 8 and 9 illustrate the bonding of the top package to the bottom package; and

FIGS. 10 and 11 are cross-sectional views of intermediate stages in the formation of a bottom package in accordance with an alternative embodiment, wherein a transfer molding method is used to apply a molding compound.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The making and using of the embodiments of the disclosure are discussed in detail below. It should be appreciated, however, that the embodiments provide many applicable inventive concepts that can be embodied in a wide variety of specific contexts. The specific embodiments discussed are merely illustrative, and do not limit the scope of the disclosure.

A package-on-package (PoP) bonding method and the resulting package structure are provided in accordance with various embodiments. The intermediate stages of manufacturing a package structure in accordance with an embodiment are illustrated. The variations of the embodiments are then discussed. Throughout the various views and illustrative embodiments, like reference numbers are used to designate like elements.

Referring to FIG. 1, package component 10 is provided. Package component 10 may comprise substrate 11 that is formed of a semiconductor material, such as silicon, silicon germanium, silicon carbide, gallium arsenide, or other commonly used semiconductor materials. Alternatively, substrate 11 is formed of a dielectric material. Package component 10 is configured to electrically couple metal bumps 12 on first surface 10A to metal features such as bond pads 16 on second surface 10B opposite first surface 10A. Accordingly, package component 10 may include metal lines/vias 14 therein. In an embodiment, package component 10 is an interposer. In alternative embodiments, package component 10 is a package substrate.

Die 20 is bonded to package component 10 through metal bumps 12. Metal bumps 12 may be solder bumps or other types of metallic metal bumps. Throughout the description, metal bumps 12 are alternatively referred to as solder bumps 12. Die 20 may be a device die comprising integrated circuit devices, such as transistors, capacitors, inductors, resistors (not shown), and the like, therein. Furthermore, die 20 may be a logic die comprising core circuits, and may be, for example, a center computing unit (CPU) die, or a memory die. The bonding between die 20 and metal bumps 12 may be a solder bonding or a direct metal-to-metal (such as a copper-to-copper) bonding. An underfill (not shown) may be dispensed into the gaps between die 20 and package component 10.

Referring to FIG. 2, molding compound 24 is molded onto die 20 and package component 10 using, for example, compressive molding or transfer molding. Accordingly, die 20 is protected by molding compound 24. In FIG. 3, solder balls 26 are mounted on bond pads 16 on surface 10B of package component 10. Solder balls 26 and die 20 may be on opposite sides of package component 10. A reflow is performed on solder balls 26. Top package 30 is thus formed. Next, as shown in FIG. 4, a flux dipping is performed to apply flux/solder paste 28 onto solder balls 26.

Referring to FIG. 5, bottom package 40 is formed. Bottom package 40 includes package component 42, which may be an interposer, a package substrate, or the like. Package component 42 is configured to electrically couple solder balls 44 and/or metal bumps 45 at the top surface to bond pads 43, which is at a bottom surface of package component 42. The metal connections from metal bumps 45 to solder balls 44 and/or bond pads 43 are not shown, although they may also exist. Furthermore, package component 42 may include metal lines and vias, both shown as 46, therein.

Die 50 is bonded to package component 42 through metal bumps 45. Metal bumps 45 may be solder bumps or other types of metallic metal bumps. Die 50 may be a device die such as a logic die or a memory die. The bonding between die 50 and bumps 45 may be a solder bonding or a direct metal-to-metal (such as a copper-to-copper) bonding. An underfill (not shown) may be dispensed into the gaps between die 50 and package component 42. Solder balls 44 may be mounted on the same side of package component 42 as die 50. Solder balls 44 have great sizes, so that the top ends 44A of solder balls 44 may be higher than top surface 50A of die 50.

FIGS. 6 and 7 illustrate the cross-sectional views of intermediate stages in a compressive molding to apply molding compound 66 on package 40. Molding compound 66 may be a resin or other types of dielectric encapsulating material. Referring to FIG. 6, a part of mould 62, which is part of compressive molding apparatus, is illustrated. Mould 62 is configured to be heated to desirable temperatures. Cavity 64 is formed in mould 62. Movable compression block 63 is under cavity 64, and is configured to be moved up and down, as symbolized by the arrows, so that the depth of cavity 64 may be changed.

Release film 60 is placed on mould 62, and extends into cavity 64. Release film 60 is relatively soft, so that when solder balls are pressed into it, the solder balls are not damaged, and the solder balls may substantially maintain their shapes. Release film 60 may be a fluorine-base film, a silicon-coated polyethylene terephthalate film, a polymethylpentene film, a polypropylene film, or the like. Mould 62 may comprise small holes (not shown), so that when vacuumed, release film 60 may have good contact with movable compression block 63, the sidewalls of mould 62 (in cavity 64), and the top surfaces of mould 62. Accordingly, substantially no air bubble is formed between release film 60 and mould 62, and between release film 60 and movable compression block 63. Release film 60 also forms a cavity, which is also shown as cavity 64. Molding compound 66, which is in a liquid form, is placed in cavity 64 and over release film 60. Bottom package 40 is then placed over cavity 64, with die 50 and solder balls 44 facing cavity 64.

Referring to FIG. 7, device die 50 and solder balls 44 are placed into cavity 64. Movable compression block 63 may also be pushed upwardly, so that molding compound 66 is pushed up to fill in the spaces between solder balls 44, and fill in the space between die 50 and solder balls 44. Molding compound 66 may also be in physical contact with surface 42A of package component 42. The amount of molding compound and the respective thickness T1 (FIG. 6) is controlled, so that solder balls 44 penetrate through molding compound 66, with solder balls 44 at least in physical contact with release film 60. In an embodiment, solder balls 44 are pressed against release film 60, with a first portion of each of solder balls 44 pressed into release film 60. A second portion of each of solder balls 44 is not pressed into release film, so that they are inside and in contact with molding compound 66. As shown in FIG. 6, depth T1 of molding compound 66 pre-placed in cavity 64 may be smaller than height H3 of solder balls 44. Die 50, on the other hand, may, or may not, be in physical contact with release film 60. In an embodiment, die 50 does not penetrate into release film 60.

Molding compound 66 is then cured, for example, by heating mould 62. During the curing step, solder balls 44 remain in physical contact with release film 60, and solder balls 44 may also remain to be pressed into release film 60. After the heating to cure molding compound 66, bottom package 40 is separated from release film 60. The resulting bottom package 40 is illustrated in FIG. 8.

As shown in FIG. 8, the portions of solder balls 44 that are in contact with, and possibly pressed into, release film 60 when the curing is performed do not have molding compound 66 thereon. The cured molding compound 66 has top surface 66A, which may be substantially flat. Top ends 44A of solder balls 44 may be at least level with, and may be higher than, top surfaces 66A. Accordingly, all solder balls 44 are exposed through cured molding compound 66. Die 50 may be buried under a thin layer of molding compound 66. Alternatively, die 50 may be exposed and having a top surface level with top surface 66A of molding compound 66. Since release film 60 is soft, pressing solder balls 44 will not cause significant change in the shape of solder balls 44, and the shape of the exposed portions of solder balls 44 may remain to be substantially rounded.

As also shown in FIG. 8, top package 30 as formed in the step shown in FIG. 4 is placed over bottom package 40. Since the compression molding in accordance with embodiments results in solder balls 44 to be exposed already, there is no need to performing a laser ablation or drilling to expose solder balls 44 from molding compound 66. Next, as shown in FIG. 9, solder balls 26 in top package 30 (please refer to FIG. 8) are placed against, and in contact with corresponding solder balls 44. A reflow is performed, so that solder balls 44 and 26 are melted to form combined solder bumps (denoted as 26/44).

FIGS. 10 and 11 illustrate the molding of molding compound 66 to package component 42 in accordance with alternative embodiments, in which molding compound 66 is molded onto package component 42 through transfer molding. Unless specified otherwise, the reference numerals in these embodiments represent like elements in the embodiments illustrated in FIGS. 1 through 9. The initial steps of this embodiment are essentially the same as shown in FIGS. 1 through 5. Next, as shown in FIG. 10, bottom package component 42 is placed on lower chassis 70 of a transfer molding equipment. Solder balls 44 face up. Release film 60 is placed over and in contact with solder balls 44. Upper chassis 72 is used to suck up and hold release film 60, which forms cavity 64. Cavity 64 may be essentially the same as cavity 64 in FIG. 6, except cavity 64 faces downwardly in FIG. 10. Solder balls 44 are pressed against release film 60, and a portion of each of solder balls 44 may be pressed into release film 60. The portions of solder balls 44 pressed into release film 60 have height H1. Die 50, on the other hand, may, or may not, be in physical contact with release film 60.

Next, as shown in FIG. 11, the air in cavity 64 is vacuumed. Molding compound 66 is then injected into cavity 64 using plunger 74, and molding compound 66 fills the spaces between package component 42, solder balls 44, die 50, and release film 60. A heating is then performed, so that molding compound 66 is cured. Bottom package 40, which now comprises molding compound 66 thereon, is then separated from release film 60. The resulting package 40 is essentially the same as shown in FIG. 8. The steps as shown in FIGS. 8 and 9 may then be performed to finish the packaging of packages 30 and 40.

By using the embodiments, after molding compound 66 is molded on package component 42, solder balls 44 are already exposed through molding compound 66. Accordingly, the step of laser ablation or drilling is saved. The manufacturing cost is reduced, and the manufacturing throughput is enhanced.

In accordance with embodiments, a method of packaging includes placing a package component over a release film, wherein solder balls on a surface of the package component are in physical contact with the release film. Next, A molding compound filled between the release film and the package component is cured, wherein during the step of curing, the solder balls remain in physical contact with the release film.

In accordance with other embodiments, a method includes providing a bottom package including a package component, a solder ball mounted over a top surface of a package component, and a device die over and bonded to the top surface of the package component. The solder ball has a top end higher than a top surface of the device die. The package component is pressed against a release film, so that a first portion of the solder ball is pressed into the release film, and a second portion of the solder ball is outside the release film. The release film forms a cavity, with the solder ball being in the cavity. A molding compound is filled into the cavity. The molding compound in the cavity is cured, wherein during the step of curing, the first portion of the solder ball remains inside the release film.

In accordance with yet other embodiments, a package includes a package component, a plurality of solder balls over and mounted onto a surface of the package component, and a molding compound over the surface of the package component. Portions of the molding compound between the plurality of solder balls have top surfaces that are lower than top ends of the plurality of solder balls.

Although the embodiments and their advantages have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the embodiments as defined by the appended claims. Moreover, the scope of the present application is not intended to be limited to the particular embodiments of the process, machine, manufacture, and composition of matter, means, methods and steps described in the specification. As one of ordinary skill in the art will readily appreciate from the disclosure, processes, machines, manufacture, compositions of matter, means, methods, or steps, presently existing or later to be developed, that perform substantially the same function or achieve substantially the same result as the corresponding embodiments described herein may be utilized according to the disclosure. Accordingly, the appended claims are intended to include within their scope such processes, machines, manufacture, compositions of matter, means, methods, or steps. In addition, each claim constitutes a separate embodiment, and the combination of various claims and embodiments are within the scope of the disclosure. 

1. A method comprising: providing a package component comprising: a device die; and solder balls, wherein the device die and the solder balls are bonded to a same side of the package component; pressing the package component against a release film, wherein first portions of the solder balls are pressed into the release film, and second portions of the solder balls and the device die are not pressed into the release film; filling a molding compound in a space between the release film and the package component, wherein the device die is submerged in the molding compound; and curing the molding compound.
 2. The method of claim 1, wherein during the step of curing, the solder balls remain in physical contact with the release film.
 3. The method of claim 1, wherein after the step of pressing, the device die contacts the release film.
 4. The method of claim 1, wherein after the step of pressing, the device die does not contact the release film, and wherein the device die is separated from the release film by the molding compound.
 5. The method of claim 1 further comprising: before the step of pressing, placing the release film on a mould, wherein a portion of the release film forms a cavity; performing the step of filling the molding compound, wherein the molding compound is filled into the cavity; and after the step of filling the molding compound, performing the step of pressing the package component.
 6. The method of claim 1, wherein the step of pressing the package component is performed before the step of filling the molding compound.
 7. The method of claim 1, wherein the device die is bonded on the package component through additional solder balls that have sizes smaller than the solder balls.
 8. The method of claim 1 further comprising: after the step of curing, separating the package component and the molding compound from the release film.
 9. A method comprising: providing a first package comprising: a first package component; a first device die bonded to a surface of the package component; and a first solder ball over the surface of the first package component adjacent to the first device die, wherein the first solder ball has a top end higher than a top surface of the first device die; placing a release film on a mould, wherein the release film forms a cavity; filling a molding compound into the cavity; placing the first package onto the molding compound by facing the first solder ball and the first device die toward the cavity; and pressing the package component against the release film, so that a top portion of the first solder ball is pressed into the release film, and the first device die is separated from the release film by the molding compound.
 10. The method of claim 9 further comprising: after the step of pressing, curing the molding compound, wherein the top portion of the first solder ball remains inside the release film during curing.
 11. The method of claim 9, wherein the step of providing the first package comprises bonding the first device die on the surface of the first package component by forming metal bumps.
 12. The method of claim 9 further comprising: after the step of curing, separating the first package and the molding compound from the release film.
 13. The method of claim 12 further comprising, after the step of separating, bonding a second package to the first package through the solder ball.
 14. The method of claim 13, wherein the second package comprises: a second package component having a first surface and a second surface opposite to the first surface; a second device die bonded to the first surface of the second package component; and a second solder ball over the second surface of the second package component, wherein the first solder ball has a top end higher than a top surface of the first device die.
 15. The method of claim 14, wherein the second solder ball of the second package is bonded to the first solder ball of the first package.
 16. A package comprising: a package component; device die bounded on to a surface of the package component; a plurality of solder balls formed on the surface of the package component adjacent to the device die; and a molding compound over the surface of the package component, covering the device die and exposing the top ends of the plurality of solder balls.
 17. The package of claim 16, wherein the device die is bonded onto the surface of the package component through a plurality of metal bumps.
 18. The package of claim 16, wherein the top ends of the plurality of solder balls have substantially rounded surfaces.
 19. The package of claim 16, wherein the top surfaces of the molding compound between the plurality of the solder balls are leveled with each other.
 20. The package of claim 16, wherein the top surface of the molding compound over the device die is substantially flat. 